RFR: JDK-8198862 Stop doing funky compilation stuff for dtrace
Magnus Ihse Bursie
magnus.ihse.bursie at oracle.com
Fri Mar 2 11:10:08 UTC 2018
On 2018-03-02 03:01, David Holmes wrote:
> Hi Magnus,
> On 1/03/2018 10:48 AM, Magnus Ihse Bursie wrote:
>> We're doing a lot of weird compilation stuff for dtrace. With this
>> patch, most of the weirdness is removed. The remaining calls to $(CC)
>> -E has been changed to $(CPP) to clarify that we do not compile, we
>> just use the precompiler.
>> One of the changes I made was to actually split up the last and final
>> dtrace call into a separate preprocessing step. However, this uses
>> the solaris studio preprocessor instead of the ancient system
>> preprocessor, which has changed behavior. A string like (&``_var) is
>> now expanded to (& ` ` _var), which is not accepted by dtrace. :-( I
>> have worked around this by adding the preprocessed output, without
>> the spaces, in two places. If anyone wants to dig deeper into dtrace
>> script file syntax, or C preprocessor magic, to avoid this, let me
>> know... (I'll just state that the "obvious" solution of sending -Xs
>> to the preprocessor to get old-style behavior does not work: this
>> just makes the solaris studio preprocessor call the ancient
>> preprocessor in turn, and we've gained nothing...)
>> Bug: https://bugs.openjdk.java.net/browse/JDK-8198862
> Why did you rename generateJvmOffsetsMain.c to
> generateJvmOffsetsMain.cpp? It isn't a C++ program, it's just a C
Yes, but so are generateJvmOffsets.cpp. :-& There was no point in mixing
a .cpp and .c file for this trivial build tool helper. In fact, I don't
even understand why they are two separate files -- if I get the
blessings from someone in hotspot, I'll gladly just concatenate them
into a single file.
> I agree the logic is quite confusing. I think this build logic was
> victim of the CPP_FLAGS (meaning C preprocessor) to CXX_FLAGS (meaning
> C++ flags) renaming. But this is a trivial C program and should
> require trivial C compiler flags. I don't see it should be being built
> with all the JVM_CFLAGS. The latter may be harmless but it seems wrong
> to lump this in together with other things.
Actually, no. Or, maybe it was a victim of CPP_FLAGS/CXX_FLAGS
confusion, too. But the JVM_CFLAGS *are* needed. Otherwise I'd removed
them, trust me. And I would have moved the entire piece of code to
gensrc, where it belongs. (This is just about compiling a build tool
that will generate source code that should be later compiled, typical
But, this file includes a lot of hotspot include files. And for that to
work, we need the -I and -D flags from JVM_CFLAGS. We probably don't
need any other parts of the JVM_CFLAGS, so in theory, we could probably
split JVM_CFLAGS into a "defines and include paths" part, and a "rest"
part. But I would not bet on it, suddenly you'd have some kind of option
(-xc99?) that modifies the parsing of the include files...
This is the general problem with all dtrace stuff, it needs to poke it's
fingers deep down in the libjvm. :(
> ! # Since we cannot generated JvmOffsets.cpp as part of the gensrc
> Comment doesn't read right.
Typo, should be "generate". I'll fix.
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